An intervention study will be conducted on 80-120 overweight children that will be randomized into one intervention and one control group. An intervention during two years will encourage long term healthy habits regarding diet and physical activity through group meetings and supervision. Information about food habits will be collected through questionnaires, interviews and diaries. Measurement of physical activity and energy expenditure will be made with Sense Wear and double labeled water, and will be used to validate reported food intake. Further, anthropometric measurements and blood samples will be collected.